A mixer truck carries mortar, ready-mixed concrete and the like (hereinafter, referred to as “fresh concrete”) in a mixer drum rotatably mounted on a chassis and transports these from a fresh concrete factory to a construction site.
The mixer truck sets the mixer drum constantly in positive rotation to prevent quality degradation and solidification of the fresh concrete in transporting the fresh concrete. By the positive rotation of the mixer drum, a plurality of spiral blades mounted in the mixer drum constantly keeps mixing the fresh concrete. Further, the mixer truck can discharge the fresh concrete in the mixer drum by setting the mixer drum in negative rotation in a direction opposite to the positive rotation. The mixer truck supplies the fresh concrete to a placement location by setting the mixer drum in negative rotation upon reaching a concrete placement site.
As just described, the mixer truck needs to constantly rotate the mixer drum until the fresh concrete is discharged after being poured into the mixer drum. An engine of the mixer truck is generally used as a drive source used for the rotation of the mixer drum. Specifically, the rotational power of the engine is transmitted to a hydraulic pump via a PTO (Power Take Off), pressure oil discharged from the hydraulic pump is supplied to a hydraulic motor and the mixer drum is driven and rotated by the rotation of the hydraulic motor.
In a mixer drum driving device for driving a mixer drum only by an engine, the rotation speed of the engine needs to be increased particularly in the case of rotating the mixer drum at a high speed. If the rotation speed of the engine is increased, noise is generated and the amount of fuel consumption increases.
Further, since the mixer drum needs to be constantly kept in rotation for reasons such as the prevention of solidification while fresh concrete is carried in the mixer drum, the engine cannot be stopped. Thus, even if the mixer truck arrives at a placement site, the engine needs to continue to be driven although a mixer truck is in park if the mixer truck is waiting to discharge the fresh concrete.
Accordingly, JP2007-278430A discloses a mixer drum driving device for driving and rotating a mixer drum by driving an auxiliary hydraulic pump by a motor in accordance with the drive of the hydraulic pump by an engine.